JP6570255B2 - Control device and control method for reducing agent injection device - Google Patents

Description

  The present invention relates to a control device and a control method for a reducing agent injection device for controlling a reducing agent injection device that supplies a reducing agent to an exhaust passage of an internal combustion engine.

NO _x (nitrogen oxide) is contained in the exhaust gas of an internal combustion engine such as a diesel engine mounted on a vehicle. As an apparatus for purifying exhaust by decomposing the reduced to nitrogen and water or the like such NO _X, urea SCR (Selective Catalystic Reduction) system has been put into practical use. The urea SCR system is a system that decomposes NO _x by reacting NO _x in exhaust with ammonia using an aqueous urea solution as a reducing agent.

Such a urea SCR system includes a selective reduction catalyst disposed in an exhaust passage and a reducing agent injection device for supplying a urea aqueous solution to an exhaust passage upstream of the selective reduction catalyst. The selective reduction catalyst is a catalyst having a function of adsorbing ammonia generated by decomposition of an aqueous urea solution and promoting a reduction reaction between NO _x and ammonia in exhaust gas flowing in. The reducing agent injection device includes a pump that pumps the urea aqueous solution stored in the storage tank, an injection valve that injects the urea aqueous solution pumped by the pump, and a control device that controls the pump and the injection valve. .

  The aqueous urea solution used in the urea SCR system has different freezing points depending on its concentration. Even at the lowest freezing point, the temperature is about minus 11 ° C. Therefore, when the internal combustion engine is stopped, the urea aqueous solution is stored from the system so that the urea aqueous solution coagulates while the vehicle is stopped and the volume expands to prevent damage to the pump, the injection valve, and the piping through which the urea aqueous solution flows. It is collected in the tank. The recovered urea aqueous solution is refilled into the system at the next start of the internal combustion engine.

  In the urea SCR system, even when the internal combustion engine is in operation, if the urea aqueous solution is not injected for a long period of time, the urea aqueous solution adhering to the injection valve is heated by the heat transmitted from the exhaust pipe. Then, the water may evaporate and the urea aqueous solution may crystallize. When the crystallization of the urea aqueous solution occurs, the valve body of the injection valve is fixed, which may cause malfunction of the injection valve. Therefore, a technique for cooling the injection valve by injecting a predetermined amount of urea aqueous solution from the injection valve and transferring heat of the injection valve to the urea aqueous solution has been proposed.

  For example, in Patent Document 1, based on the exhaust gas temperature when the engine is stopped, a cooling time required for the injection valve to be lowered to a temperature at which urea water is hardly deteriorated is set, and the cooling is performed after the engine is stopped. An SCR system that performs cooling for injecting a predetermined amount of urea water from an injection valve until time elapses is disclosed.

JP 2012-17687 A

In the SCR system, the injection amount of the urea aqueous solution is determined so that ammonia generated by the decomposition of the urea aqueous solution does not flow downstream from the selective reduction catalyst. For example, the injection amount of the aqueous urea solution includes the ammonia amount corresponding to the NO _x amount in the exhaust gas of the internal combustion engine, the ammonia adsorption amount according to the temperature of the selective reduction catalyst, and the ammonia adsorption amount in the current selective reduction catalyst. Calculated based on Specifically, for example, the adsorption amount of the reducing agent is set so that the actual adsorption rate becomes the target adsorption rate, with about 70 to 80% of the ammonia adsorbable amount corresponding to the temperature of the selective reduction catalyst as the target adsorption rate. Is calculated.

  However, in the cooling control described in Patent Document 1, the cooling control for injecting a predetermined amount of urea water is performed based only on the cooling time for reducing the temperature of the injection valve. Therefore, as a result of the cooling control, ammonia may be generated exceeding the amount of ammonia that can be adsorbed by the selective reduction catalyst, and ammonia may flow out downstream of the selective reduction catalyst.

  The present invention has been made in view of the above problems, and an object of the present invention is to reduce the downstream side of the reduction catalyst when performing control to cool the injection valve by injecting the reducing agent. It is an object of the present invention to provide a control device and a control method for a reducing agent injection device capable of preventing components from flowing out.

In order to solve the above-described problems, according to one aspect of the present invention, the internal combustion engine is disposed upstream of a reduction catalyst disposed in an exhaust passage via an injection valve attached to an exhaust pipe of the internal combustion engine. An injection valve temperature for determining a temperature of the injection valve based on information related to the temperature of the injection valve in a control apparatus for controlling a reduction agent injection apparatus that supplies a reducing agent for purifying NO _x in exhaust gas A calculation unit; an injection valve temperature determination unit for determining whether or not a temperature of the injection valve exceeds a predetermined upper limit threshold; and when the temperature of the injection valve exceeds the upper limit threshold, injection and _the amount of NO _X increases control unit for _the amount of NO _X increase control for increasing the amount of NO _X, and when the temperature of the injector exceeds the upper threshold, the reducing agent for cooling the injection valve Cooling injection control unit for performing cooling injection control It comprises a control device of the reducing agent injection apparatus is provided.

The cooling injection control unit may execute the cooling injection control after a predetermined time has elapsed since the execution of the NO _x amount increase control.

  The upper limit threshold may be a value smaller than the upper limit of the usable temperature range of the injection valve.

  The injection valve temperature determination unit further determines whether or not the temperature of the injection valve is below a predetermined release threshold, and the cooling injection control unit is a period until the temperature of the injection valve falls below the release threshold The cooling injection control may be repeated.

  The release threshold value may be a value smaller than the upper limit threshold value.

NO _X for performing NO _X purification injection control for determining the injection amount of the reducing agent based on at least the NO _X amount in the exhaust gas of the internal combustion engine and injecting the reducing agent for purifying NO _X in the exhaust gas. comprising a purification injection control unit, the NO _X purification injection control unit, the rear of the cooling injection control ends, and the amount of NO _X is increased by the amount of NO _X increase control, it is injected by the cooling injection control The injection amount of the reducing agent may be obtained based on the injection amount of the reducing agent.

When the reduction catalyst is a catalyst that retains the reducing component derived from the reducing agent and purifies NO _x in the exhaust flowing into the exhaust gas by the reducing component, the NO _x purification injection control unit includes the cooling component. After completion of the injection control, the amount of the reducing agent corresponding to the amount of the reducing component necessary for the purification of the NO _x increased by the NO _x amount increase control and the injection by the cooling injection control The reducing agent injection amount may be obtained in consideration of the difference between the reducing agent injection amount and the reducing agent injection amount.

A reducing agent that supplies a reducing agent for purifying NO _{x in} the exhaust gas of the internal combustion engine to the upstream side of the reduction catalyst disposed in the exhaust passage via an injection valve attached to an exhaust pipe of the internal combustion engine In the control method of the reducing agent injection device for cooling the injection valve in the injection device, whether or not the temperature of the injection valve obtained based on the information related to the temperature of the injection valve exceeds a predetermined upper limit threshold value determining a, when the temperature of the injector exceeds the upper threshold value, and performing _the amount of NO _X increase control for increasing the amount of NO _X in the exhaust gas of the internal combustion engine, the temperature of the injection valve Performing a cooling injection control that injects the reducing agent for cooling the injection valve when the upper limit threshold is exceeded.

  As described above, according to the present invention, when the control for cooling the injection valve is performed by injecting the reducing agent, the reducing component can be prevented from flowing out downstream of the reduction catalyst.

It is the schematic which shows the exhaust gas purification system provided with the reducing agent injection apparatus concerning 1st Embodiment. It is a block diagram which shows the structural example of the control apparatus of the reducing agent injection apparatus concerning the embodiment. It is a flowchart which shows the control method of the reducing agent injection apparatus concerning the embodiment. It is a time chart for demonstrating the control method of the reducing agent injection apparatus concerning the embodiment. It is a flowchart which shows the control method of the reducing agent injection apparatus concerning 2nd Embodiment.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<< 1. First embodiment >>
<1-1. Overall configuration of exhaust purification system>
First, an overall configuration of an exhaust purification system 10 including a reducing agent injection device 20 according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is an explanatory diagram showing a schematic configuration of the exhaust purification system 10. The exhaust gas purification system 10 includes a particulate filter 17 for collecting particulate matter (PM) in exhaust gas and a urea SCR system for reducing NO _x in the exhaust gas. The urea SCR system includes a reduction catalyst 13 and a reducing agent injection device 20 that supplies a reducing agent into an exhaust passage on the upstream side of the reduction catalyst 13. The exhaust purification system 10 is configured as a system that purifies exhaust by capturing PM in exhaust and reducing NO _x in the exhaust.

(1-1-1. Particulate filter)
The particulate filter 17 collects PM such as soot contained in the exhaust gas when the exhaust gas passes through the particulate filter 17. The particulate filter 17 can be, for example, a honeycomb structure filter made of a ceramic material, but is not limited to such a filter, and a known filter can be used. In the particulate filter 17, regeneration control is performed to burn (oxidize) PM at an appropriate time so that the trapped PM does not clog the filter as time passes.

  For example, when the pressure difference between the upstream side and the downstream side of the particulate filter 17 exceeds a predetermined threshold, it is determined that the amount of PM trapped in the particulate filter 17 has reached a predetermined amount, and regeneration control is performed. It may be executed. Further, regeneration control may be executed when it is estimated that the amount of PM trapped in the particulate filter 17 has reached a predetermined amount based on the operating state of the internal combustion engine 5. Furthermore, regeneration control may be performed when the ignition switch is turned off at the end of use of the vehicle.

  The regeneration control is performed by passing high-temperature exhaust through the particulate filter 17 or heating the particulate filter 17 with a heating device such as an electric heater or a flame burner. However, the reproduction control means is not particularly limited. For example, the PM in the particulate filter 17 can be burned by passing the high-temperature exhaust gas through the particulate filter 17 using the oxidation catalyst 19 disposed on the upstream side of the particulate filter 17.

  Specifically, when the particulate filter 17 is regenerated, the internal combustion engine 5 performs post-injection after the main injection, thereby increasing unburned fuel contained in the exhaust gas. Since the unburned fuel is oxidized in the oxidation catalyst 19, the exhaust temperature rises due to the oxidation heat at this time. When this high-temperature exhaust gas flows into the particulate filter 17, the PM collected by the particulate filter 17 is burned, and the particulate filter 17 is regenerated.

(1-1-2. Urea SCR system)
The urea SCR system is a system that reduces and decomposes NO _x in exhaust using an aqueous urea solution as a reducing agent. The urea aqueous solution may be a 32.5% concentration urea aqueous solution having the lowest freezing temperature, for example. The freezing temperature in this case is about minus 11 ° C. Such an aqueous urea solution is known to crystallize due to evaporation of moisture and the like.

The reduction catalyst 13 selectively reduces NO _x contained in the exhaust gas of the internal combustion engine 5 using a reducing agent. In the present embodiment, ammonia generated by decomposition of the urea aqueous solution injected by the reducing agent injection device 20 is adsorbed by the reduction catalyst 13, and NO _x in the exhaust gas flowing into the reduction catalyst 13 reacts with ammonia. Reduced. The reduction catalyst 13 has a characteristic that the amount of ammonia that can be adsorbed decreases as the catalyst temperature increases. Further, the reduction catalyst 13 has a characteristic that the reduction efficiency of NO _x increases as the actual ammonia adsorption rate with respect to the adsorbable amount increases. In this specification, not only the urea aqueous solution injected from the injection valve 31 into the exhaust passage, but also ammonia generated by decomposing the urea aqueous solution may be referred to as “reducing agent”.

The reducing agent injection device 20 injects a urea aqueous solution as a reducing agent into the exhaust passage upstream of the reduction catalyst 13. The injection amount of the urea aqueous solution is controlled so that NO _x or ammonia does not flow out downstream of the reduction catalyst 13 based on the concentration of NO _x contained in the exhaust gas, the amount of ammonia that can be adsorbed by the reduction catalyst 13, and the like. The

A temperature sensor 15 for detecting the exhaust temperature Tgas is attached to the exhaust pipe 11 upstream of the reduction catalyst 13. The exhaust gas temperature Tgas detected by the temperature sensor 15 is also used for estimating the temperature of the reduction catalyst 13. In addition to this, the exhaust pipe 11 may be provided with a NO _x concentration sensor, an ammonia sensor, or the like (not shown).

(1-1-3. Configuration Example of Reducing Agent Injection Device)
Next, an example of the configuration of the reducing agent injection device 20 will be described in detail. As shown in FIG. 1, the reducing agent injection device 20 sucks up the injection valve 31 fixed to the exhaust pipe 11 on the upstream side of the reduction catalyst 13 and the urea aqueous solution in the storage tank 50, and faces the injection valve 31. And a pump 41 for pumping. The pump 41 and the injection valve 31 are driven and controlled by the control device 60. The control device 60 can acquire information related to the operating state such as the fuel injection amount, injection timing, and engine speed of the internal combustion engine 5.

  In the exhaust gas purification system 10 shown in FIG. 1, the control device 60 acquires information directly from the internal combustion engine 5. For example, the internal combustion engine is connected to the internal combustion engine via a bus wiring such as a CAN (Controller Area Network). Information may be acquired from the control device 5.

  The pump 41 is composed of, for example, an electric diaphragm pump or a motor pump. The output of the pump 41 is controlled based on a control signal output from the control device 60. In the present embodiment, the control device 60 feedback-controls the output of the pump 41 so that the pressure of the urea aqueous solution supplied to the injection valve 31 detected by a pressure sensor (not shown) is maintained at a predetermined target value. .

  The injection valve 31 is an electromagnetic injection valve that can be switched between open and closed by energization control. The injection valve 31 includes a coil, and has a structure in which the valve body is moved and opened by a magnetic force generated by energizing the coil. As described above, in this embodiment, since the pressure of the urea aqueous solution supplied to the injection valve 31 is maintained at a constant pressure, the control device 60 adjusts the valve opening time according to the target injection amount of the urea aqueous solution. . The usable temperature of the injection valve 31 is limited. The usable temperature can be limited due to, for example, the heat resistant temperature of the coil portion, the heat resistant temperature of the resin portion that covers the coil portion, the temperature at which the urea aqueous solution can be denatured, and the like.

  Therefore, the injection valve 31 is held in a cooling cover (not shown), and the cooling water of the internal combustion engine 5 can flow through the cooling cover. The cooling water passage in the cooling cover constitutes a part of the cooling water circulation passage 35. The cooling water circulation passage 35 branches off from the cooling passage of the cooling device provided in the internal combustion engine 5 and joins the cooling passage of the internal combustion engine 5 again via the cooling cover of the injection valve. After the internal combustion engine 5 is started, cooling water always flows through the cooling water circulation passage 35. Therefore, during the operation of the internal combustion engine 5, in a situation where the injection valve 31 is heated by high-temperature exhaust heat or the like, cooling water flows through the cooling water circulation passage 35, and overheating of the injection valve 31 is suppressed.

  However, overheating of the injection valve 31 may not be suppressed only by the cooling water circulating in the cooling water circulation passage 35 during a period in which the exhaust gas temperature is controlled to be high, such as during regeneration control of the particulate filter 17. In such a case, the control device 60 according to the present embodiment performs the cooling injection in which the urea aqueous solution is injected from the injection valve 31 and the injection valve 31 is cooled by heat transfer. In the present embodiment, the usable temperature is defined by the temperature of the injection valve 31 estimated by the control device 60.

<1-2. Control device>
Next, a configuration example of the control device 60 used for controlling the reducing agent injection device 20 according to the present embodiment will be described. FIG. 2 is a block diagram functionally showing a part related to the cooling injection control of the injection valve 31 in the configuration of the control device 60. Such a control device 60 is mainly composed of a known microcomputer or the like.

The control device 60 includes an injection valve temperature calculation unit 101, an injection valve temperature determination unit 103, an NO _x amount increase control unit 105, a cooling injection control unit 107, and an NO _x purification injection control unit 109. Specifically, each of these units is realized by executing a program by a microcomputer. The control device 60 according to the present embodiment receives a detection signal from the temperature sensor 15 and information related to the operating state of the internal combustion engine 5 directly or via a bus wiring such as CAN. The control device 60 includes a storage element (not shown) such as a RAM (Random Access Memory) and a ROM (Read Only Memory). These storage elements store programs executed by the microcomputer, calculation results, detection results, and the like.

(1-2-1. NO _x purification control unit)
The NO _X purification injection control unit 109 executes NO _X purification injection control for injecting an aqueous urea solution in order to purify NO _X contained in the exhaust gas of the internal combustion engine 5. Hereinafter, an example of a method for calculating the injection amount of the reducing agent will be described.

For example, the NO _X purification injection control unit 109 obtains the ammonia amount necessary for reducing the NO _X based on the NO _X amount in the exhaust gas of the internal combustion engine 5, and with respect to the target adsorption amount of the reduction catalyst 13. Thus, the excess or deficiency of ammonia can be obtained, and the amount of urea aqueous solution corresponding to the sum of these can be set as the target injection amount. _The amount of NO _X in the exhaust gas, NO _X concentration Nu is estimated based on the operating state of the internal combustion engine 5, or to the NO _X concentration Nu detected by the NO _X sensor, the amount of NO _X obtained by multiplying the exhaust gas flow rate Can be used. Then, the NO _X purification injection control unit 109 obtains an ammonia amount corresponding to the calculated NO _X amount.

Further, the NO _X purification injection control unit 109 obtains the current adsorbable amount of the reduction catalyst 13 from the estimated catalyst temperature, and sets, for example, 70 to 80% of the adsorbable amount as the target adsorption amount. For example, the NO _X purification injection control unit 109 estimates the temperature of the reduction catalyst 13 based on detection information of the temperature sensor 15 or other temperature sensors not shown. By setting the target adsorption rate to 70 to 80%, the adsorption rate is maintained relatively high, and the NO _x reduction efficiency is increased. It is possible to prevent the adsorbable amount from dropping below the current ammonia adsorption amount.

Then, the NO _X purification injection control unit 109 reads the current ammonia adsorption amount from the integration result so far, finds the excess or deficient ammonia amount with respect to the target adsorption amount, and adds it to the previously obtained ammonia amount. When the current ammonia adsorption amount is insufficient with respect to the target adsorption amount, the excess / deficiency ammonia amount is a positive value. When the current ammonia adsorption amount is excessive with respect to the target adsorption amount, The excess / deficiency of ammonia is a negative value.

The NO _x purification injection control unit 109 drives and controls the injection valve 31 with the amount of urea aqueous solution corresponding to the calculated ammonia amount as a target injection amount. As described above, since the pressure of the urea aqueous solution supplied to the injection valve 31 is controlled to be kept constant, the NO _X purification injection control unit 109 adjusts the injection time according to the target injection amount. . By executing the NO _x purification injection control in this manner, the ammonia adsorption rate in the reduction catalyst 13 is maintained high while the ammonia outflow to the downstream side of the reduction catalyst 13 is suppressed, and the NO _x reduction efficiency. Will improve.

Note that the method for obtaining the injection amount of the reducing agent in the NO _X purification injection control is not limited to the above example.

(1-2-2. Injection valve temperature calculation unit)
The injection valve temperature calculation unit 101 estimates the temperature Tdv of the injection valve 31 based on information related to the exhaust gas temperature Tg detected by the temperature sensor 15. The injection valve 31 can be heated by directly or indirectly transmitting the amount of heat of the exhaust. Therefore, the information detected by the temperature sensor 15 corresponds to information related to the temperature Tdv of the injection valve 31. The relationship between the exhaust temperature Tg and the temperature Tdv of the injection valve 31 varies depending on the arrangement position of the injection valve 31, the layout of the exhaust pipe 11, and the like. The estimated temperature Tdv of the injection valve 31 may be, for example, the temperature of the coil portion of the injection valve 31 or the tip temperature of the injection valve 31. The relationship between the information detected by the temperature sensor 15 and the temperature Tdv of the injection valve 31 can be obtained in advance by simulation or the like using an actual machine.

  The method of estimating the temperature Tdv of the injection valve 31 is not limited to the above example. The injection valve temperature calculation unit 101 may estimate the temperature Tdv of the injection valve 31 by obtaining the amount of heat applied to the injection valve 31 using information detected by the temperature sensor 15. Moreover, if a temperature sensor can be attached to the predetermined position of the injection valve 31, the injection valve temperature calculation part 101 may estimate the temperature Tdv of the injection valve 31 based on the detection information of the said temperature sensor. Further, the injection valve temperature calculation unit 101 may estimate the temperature of the injection valve 31 based on the relationship between the operating state of the internal combustion engine 5 and the circulation amount of the cooling water.

(1-2-3. Injection valve temperature determination unit)
The injection valve temperature determination unit 103 determines whether or not the temperature Tdv of the injection valve 31 estimated by the injection valve temperature calculation unit 101 exceeds a predetermined upper threshold Tthr_x. The upper threshold Tthr_x can be set based on the usable temperature of the injection valve 31 described above. The upper limit threshold value Tthr_x is a determination threshold value for starting execution of the cooling injection control, and is preferably set to a value smaller than the upper limit value of the usable temperature. Thereby, even if it is a case where the start timing of the cooling injection control and the timing at which the temperature Tdv of the injection valve 31 starts decreasing, the temperature Tdv of the injection valve 31 can be prevented from exceeding the usable temperature. .

(1-2-4. NO _x amount increase control unit)
When the temperature Tdv of the injection valve 31 exceeds the upper limit threshold value Tthre_x, the NO _X amount increase control unit 105 executes NO _X amount increase control for increasing the NO _X amount in the exhaust gas of the internal combustion engine 5. If such NO _x amount increase control is executed, the ammonia adsorbed on the reduction catalyst 13 is used for the NO _x reduction reaction, and the ammonia adsorption amount on the reduction catalyst 13 can be reduced. Therefore, even when the urea injection solution for cooling the injection valve 31 is injected by executing the cooling injection control, the generated ammonia is adsorbed by the reduction catalyst 13 and is downstream of the reduction catalyst 13. The outflow of ammonia to the is suppressed.

_The amount of NO _X increases control unit 105, for example, sends a control command to the control device of the internal combustion engine 5, by controlling the operating state of the internal combustion engine 5, by improving the combustion efficiency, increase the amount of NO _X in the exhaust gas Can be made. Specifically, the NO _x amount increase control unit 105 improves the combustion efficiency and increases the NO _x amount by controlling the fuel injection timing or decreasing the recirculation amount of the EGR gas. Can do. The method for increasing the NO _x amount is not particularly limited.

At this time, in consideration of the current ammonia adsorption amount in the reduction catalyst 13, the amount of NO _x to be increased may be assumed and the NO _x amount increase control may be executed. In this way, it is possible to suppress NO _X from flowing out downstream of the reduction catalyst due to the ammonia adsorption amount becoming zero. On the other hand, in this embodiment, the injection of the urea aqueous solution for cooling the injection valve 31 is performed a preset number of times. Therefore, _the amount of NO _X increases control unit 105, also as can be purified amount of NO _X more of the NO _X is to perform the amount of NO _X increases control as discharged by urea aqueous solution injected by the cooling injection control Good.

(1-2-5. Cooling injection control unit)
The cooling injection control unit 107 performs urea aqueous solution injection control to cool the injection valve when the temperature Tdv of the injection valve 31 exceeds the upper limit threshold value Tthre_x. Specifically, as described above, the NO _X purification injection control unit 109 calculates the target injection amount of the urea aqueous solution in order to purify NO _X in the exhaust during the period when the cooling injection control is not executed, and the urea _X The injection control of the aqueous solution is executed. The cooling injection control unit 107 moves the heat of the injection valve 31 to the urea aqueous solution by lowering the temperature Tdv of the injection valve 31 by injecting the urea aqueous solution separately from the NO _x purification injection control.

At the time of injection control of the urea aqueous solution by the NO _X purification injection control unit 109, the ammonia adsorption rate in the reduction catalyst 13 is controlled to 70 to 80%. Therefore, even if the amount of ammonia is increased by the cooling injection control, Immediately ammonia does not flow out downstream of the reduction catalyst 13. Further, since the NO _x amount increase control is also started, the ammonia adsorbed on the reduction catalyst 13 can be reduced by the increased NO _x after a predetermined time has elapsed. Therefore, even when the cooling injection control is executed, the outflow of ammonia to the downstream side of the reduction catalyst 13 can be suppressed.

However, the amount of NO _X increase control, so that the adsorption amount of ammonia in the reduction catalyst 13 is made the cooling injection after reduction, so that the cooling jet from the execution of the NO _X amount increase control after a predetermined time has elapsed is performed It may be. In this way, the ammonia generated from the urea aqueous solution injected by the cooling injection suppresses the ammonia adsorption amount in the reduction catalyst 13 from reaching the adsorbable amount and flowing out to the downstream side of the reduction catalyst 13. can do. The time for delaying the execution of the cooling injection can be set in consideration of, for example, the time from the output of the NO _x amount increase control execution command until the increased NO _x starts flowing into the reduction catalyst 13. . For example, the time for delaying the execution of the cooling injection may be 3 to 10 seconds.

  In addition, the temperature of the injection valve 31 that decreases due to the execution of the cooling injection can be obtained in advance by simulation or the like using an actual machine. Therefore, the injection amount required to make the temperature Tdv of the injection valve 31 sufficiently lower than the upper limit threshold value Tthr_x from the state in which the temperature Tdv of the injection valve 31 exceeds the upper limit threshold value Tthr_x can be obtained in advance. Therefore, in the present embodiment, the cooling injection control unit 107 executes injection for a preset injection time at a preset number of times.

The cooling injection control unit 107 sends information on the injection amount of the urea aqueous solution in the cooling injection control to the NO _X purification injection control unit 109. Further, the NO _X purification injection control unit 109 continues the calculation for the NO _X amount discharged during the NO _X amount increase control. Therefore, NO _X purification injection control unit 109, after the cooling injection control, the basis of the amount of NO _X is increased by _the amount of NO _X increase control, in the injection amount of the urea aqueous solution injected by the cooling injection control Thus, the injection amount of the urea aqueous solution is obtained. That is, the NO _X purification injection control unit 109 is injected by the cooling injection control from the amount of urea aqueous solution corresponding to the amount of ammonia necessary for purification of the amount of NO _X increased by the NO _X amount increase control. The injection amount of the urea aqueous solution is obtained so that the difference obtained by subtracting the injection amount of the urea aqueous solution is compensated. As a result, even after the cooling injection control, the ammonia adsorption rate in the reduction catalyst 13 can be maintained high, and NO _x can be efficiently purified.

<1-3. Control Method of Reducing Agent Injection Device>
Next, an example of a control method of the reducing agent injection device executed by the control device 60 according to the present embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 is a flowchart showing a control method for the reducing agent injection apparatus according to the present embodiment. FIG. 4 shows the NO _x amount and the injection valve 31 when the control method for the reducing agent injection apparatus according to the present embodiment is executed. It is a time chart which shows transition of temperature and ammonia slip amount. Further, in FIG. 4, transitions of the NO _x amount and the ammonia slip amount when the control method for the reducing agent injection device according to the present embodiment is not executed are indicated by broken lines.

First, in step S10, the control device 60 determines whether or not the estimated temperature Tdv of the injection valve 31 exceeds an upper limit threshold value Tthr_x set in advance. When the temperature Tdv of the injection valve 31 is equal to or lower than the upper limit threshold Tthre_x, the control device 60 repeats the determination of the temperature Tdv of the injection valve 31 (period until t1 in FIG. 4). If the temperature Tdv of the injection valve 31 exceeds the upper limit threshold value Tthre_x at the time point t1 (S10: Yes), the control device 60 proceeds to step S20 and instructs execution of the NO _x amount increase control. For example, a control command is output to the control device for the internal combustion engine 5 so as to enter an operation state in which the amount of NO _{x in} the exhaust gas increases. Next, in step S30, the control device 60 starts cooling injection control for reducing the temperature Tdv of the injection valve 31.

After instructing the start of the NO _X amount increase control, with a slight delay, at time t2, _the amount of NO _X in the exhaust gas is increased. Although the execution of the cooling injection is started from the time t1 to the time t2, the ammonia flows out to the downstream side of the reduction catalyst 13 until the adsorption amount of ammonia in the reduction catalyst 13 reaches the adsorbable amount. Never do. Therefore, even after the time t2, the ammonia slip amount does not increase immediately. Thereafter, the temperature Tdv of the injection valve 31 starts to decrease due to the effect of the cooling injection control.

In the present embodiment, the NO _x amount increase control and the cooling injection control are executed in a preset period from the time t1 to the time t3. At the time point t3 when these controls are stopped, the temperature of the injection valve 31 is returned to a relatively low temperature. Therefore, the injection valve 31 does not cause crystallization of the urea aqueous solution.

On the other hand, as shown by the broken line in FIG. 4, when only the cooling injection control is executed without executing the NO _x amount increase control, the temperature Tdv of the injection valve 31 is started after the cooling injection control is started. However, after the amount of adsorbed ammonia reaches the adsorbable amount, ammonia flows out downstream of the reduction catalyst 13. Therefore, the ammonia slip amount is increasing.

As described above, according to the control device and the control method for the reducing agent injection device according to the first embodiment, the injection valve 31 is cooled when the temperature Tdv of the injection valve 31 exceeds the upper limit threshold value Tthr_x. In conjunction with the cooling injection, the control for increasing the NO _x concentration in the exhaust gas is performed. Thus, ammonia has been adsorbed by the reduction catalyst 13 is reduced by used in the reduction of increased NO _X. Thereby, it is possible to reliably suppress the ammonia adsorbable amount in the reduction catalyst 13 from exceeding the adsorbable amount by the ammonia generated from the urea aqueous solution supplied by the cooling injection.

<< 2. Second embodiment >>
Next, a control device and a control method for the reducing agent injection device according to the second embodiment will be described. The configuration of the exhaust purification system to which the control device according to the present embodiment can be applied can be the same as the configuration of the exhaust purification system according to the first embodiment. The control device according to the first embodiment performs the NO _x amount increase control and the cooling injection control in a preset period, whereas the control device according to the present embodiment controls the temperature of the injection valve 31. The cooling injection control is repeated at least until Tdv falls below a predetermined release threshold value Tthr_y. Hereinafter, the difference between the control device 60 and the control method of the reducing agent injection device 20 from the case of the first embodiment will be mainly described.

  In the present embodiment, the injection valve temperature determination unit 103 determines whether or not the temperature Tdv of the injection valve 31 has fallen below a predetermined release threshold value Tthr_y after the start of the cooling injection control. The release threshold value Tthr_y is preferably smaller than the upper threshold value Tthre_y. Thereby, for example, when the exhaust gas temperature Tg detected by the temperature sensor 15 repeats fluctuations with an extremely short period, the temperature Tdv of the injection valve 31 moves up and down across the upper limit threshold value Tthr_x, whereby the cooling injection is performed. It is possible to prevent the control from being turned on and off repeatedly. For example, the difference between the upper threshold Tthr_x and the cancellation threshold Tthr_y can be set to 10 degrees, but is not limited to this example.

In the present embodiment, the NO _x amount increase control unit 105 may increase the NO _x in the exhaust gas so that the ammonia adsorption rate in the reduction catalyst 13 decreases relatively significantly. In this way, it is possible to repeatedly execute the cooling injection control without additionally increasing the amount of NO _x until the temperature of the injection valve 31 decreases.

In the present embodiment, the cooling injection control unit 107 repeatedly executes the cooling injection control for a period until the temperature Tdv of the injection valve 31 falls below the release threshold Tthr_y. However, if an amount of urea aqueous solution that can generate ammonia that greatly exceeds the adsorption amount of ammonia decreased by the NO _x increased by the NO _x amount increase control is injected, ammonia may flow out downstream of the reduction catalyst 13. There is. Thus, cooling the injection control unit 107, if in excess of the amount the injection amount of urea water solution in the cooling injection control, corresponds to the amount of adsorption of ammonia was reduced by increased NO _X by _the amount of NO _X increasing control, It is preferable that the cooling injection is executed after the NO _x amount increase control is additionally performed.

  FIG. 5 is a flowchart showing a control method of the reducing agent injection device executed by the control device 60 of the reducing agent injection device according to the present embodiment. In this flowchart, steps S10 to S30 can be performed according to the same procedure as the control method of the reducing agent injection device according to the first embodiment. In the present embodiment, after executing the cooling injection control in step S30, the control device 60 determines in step S40 whether or not the temperature Tdv of the injection valve 31 has fallen below the release threshold value Tthre_y.

When the temperature Tdv of the injection valve 31 is lower than the release threshold value Tthre_y (S40: Yes), the process returns to step S10 without further performing the cooling injection control. On the other hand, when the temperature Tdv of the injection valve 31 is equal to or higher than the release threshold Tthre_y (S40: No), the control device 60 returns to step S30 and repeats the cooling injection control. The control device 60 repeatedly performs the cooling injection control until the temperature Tdv of the injection valve 31 falls below the release threshold value Tthr_y. Also during this time, the amount of adsorption of ammonia in the reduction catalyst 13 is less likely to exceed the adsorbable amount by increasing the amount of NO _x .

  In the time chart shown in FIG. 4, when the control according to the present embodiment is applied, the cooling injection control is turned off at the time t4 when the temperature Tdv of the injection valve 31 falls below the release threshold value Tthr_y. Therefore, there is a possibility that the injection amount of the cooling urea aqueous solution is reduced as compared with the case where the cooling injection control is executed for a predetermined time set in advance.

As described above, according to the control device and the control method for the reducing agent injection device according to the second embodiment, when the temperature Tdv of the injection valve 31 exceeds the upper limit threshold value Tthr_x, the injection valve 31 is cooled. In conjunction with the cooling injection, the control for increasing the NO _x concentration in the exhaust gas is performed. Thus, ammonia has been adsorbed by the reduction catalyst 13 is reduced by used in the reduction of increased NO _X. Thereby, it is possible to reliably suppress the ammonia adsorbable amount in the reduction catalyst 13 from exceeding the adsorbable amount by the ammonia generated from the urea aqueous solution supplied by the cooling injection.

Further, in the control device and the control method for the reducing agent injection device according to the second embodiment, when the temperature Tdv of the injection valve 31 falls below the release threshold value Tthr_y, the NO _x amount increase control and the cooling injection control are stopped. Is done. Therefore, the temperature Tdv of the injection valve 31 can be reliably lowered, and in some cases, the injection amount of the urea aqueous solution can be reduced.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 5 Engine 10 Exhaust purification system 11 Exhaust pipe 13 Reduction catalyst 15 Temperature sensor 17 Particulate filter 19 Oxidation catalyst 20 Reducing agent injection device 31 Injection valve 41 Pump 50 Storage tank 60 Control device 101 Injection valve temperature calculation part 103 Injection valve temperature determination part 105 NO _X amount increase control unit 107 Cooling injection control unit 109 NO _X purification injection control unit

Claims (7)

Reducing agent injection for supplying a reducing agent for purifying NOx in the exhaust gas of the internal combustion engine to the upstream side of the reduction catalyst disposed in the exhaust passage via an injection valve attached to the exhaust pipe of the internal combustion engine In a control device for controlling a device,
An injection valve temperature calculation unit for determining the temperature of the injection valve based on information related to the temperature of the injection valve;
An injection valve temperature determination unit for determining whether or not the temperature of the injection valve exceeds a predetermined upper limit threshold;
A NOx amount increase control unit for performing NOx amount increase control for increasing the NOx amount in the exhaust gas of the internal combustion engine when the temperature of the injection valve exceeds the upper limit threshold;
A cooling injection control unit that performs cooling injection control for injecting the reducing agent for cooling the injection valve when the temperature of the injection valve exceeds the upper limit threshold;
Equipped with a,
The cooling injection control unit, after a predetermined ammonia adsorbed on the reduction catalyst from the execution of the NOx amount increase control is to be reduced for the state time to run the cooling injection control of the reducing agent injection apparatus Control device. The control device for a reducing agent injection device according to claim 1, wherein the upper limit threshold value is smaller than an upper limit value of a usable temperature range of the injection valve. The injection valve temperature determination unit further determines whether or not the temperature of the injection valve is below a predetermined release threshold;
The cooling injection control unit for a period of up to a temperature of the injection valve is below the release threshold, repeating said cooling injection control, the control device of the reducing agent injection apparatus according to claim 1 or 2. The control device of a reducing agent injection device according to claim 3 , wherein the release threshold is a value smaller than the upper limit threshold. NOx purification injection control for determining the injection amount of the reducing agent based on at least the amount of NOx in the exhaust gas of the internal combustion engine and performing NOx purification injection control for injecting the reducing agent to purify the NOx in the exhaust gas. Part
The NOx purification injection control unit is based on the NOx amount increased by the NOx amount increase control and the injection amount of the reducing agent injected by the cooling injection control after the cooling injection control ends. The control apparatus of the reducing agent injection device according to any one of claims 1 to 4 , wherein an injection amount of the reducing agent is obtained. When the reduction catalyst is a catalyst that retains the reducing component derived from the reducing agent and purifies NOx in the exhaust flowing in by the reducing component,
The NOx purification injection control unit includes an amount of the reducing agent corresponding to an amount of the reducing component required for purification of the NOx in an amount increased by the NOx amount increase control after completion of the cooling injection control. The control device for the reducing agent injection device according to claim 5 , wherein an injection amount of the reducing agent is obtained in consideration of a difference between the amount of the reducing agent injected by the cooling injection control. Reducing agent injection for supplying a reducing agent for purifying NOx in the exhaust gas of the internal combustion engine to the upstream side of the reduction catalyst disposed in the exhaust passage via an injection valve attached to the exhaust pipe of the internal combustion engine In the control method of the reducing agent injection device for cooling the injection valve in the device,
Determining whether the temperature of the injection valve determined based on information related to the temperature of the injection valve exceeds a predetermined upper limit threshold;
Performing NOx amount increase control for increasing the NOx amount in the exhaust gas of the internal combustion engine when the temperature of the injection valve exceeds the upper limit threshold;
Performing cooling injection control for injecting the reducing agent for cooling the injection valve when the temperature of the injection valve exceeds the upper limit threshold; and
Equipped with a,
Wherein the execution of the NOx amount increase control after a lapse of the predetermined ammonia adsorbed on the reduction catalyst is reduced state time to run the cooling injection control method for controlling a reductant injection device.

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